CS 3813/718 Fall Python Programming. Professor Liang Huang.

Transcription

1 CS 3813/718 Fall 2012 Python Programming Professor Liang Huang

2 Logistics Lectures: TTh 9:25-10:40 am SB B-141 Personnel Instructor Prof. Liang Huang TA Kai Zhao Admin Xiuyi Huang Office Hours (subject to change!) LH -- SB A-328 KZ -- SB A-207 T 4-5 pm, Th 10:50-11:30am T 10:50-11:30 am, Th 4-5pm additional office hours available before quizzes/exams 2

3 Logistics - cont d Homepage vision.cs.qc.cuny.edu/huang/python-2012f/ schedule, syllabus, homework, handouts, etc. Newsgroup cs qc@googlegroups.com announcements, Q/A --> post here first! Course cs qc@gmail.com to reach both the instructor and the TA don t us individually Blackboard -- the [2nd ] worst software I ever used! grades and electronic submissions 3

4 Grades Programming Homework: 5% + 7% + 8% = 20% electronic submission; work individually: only high-level discussions are OK, and you have to declare who you discussed with grading is mostly black-box: you should follow strict I/O formats! please work on Linux or Mac; we don t support Windows users late penalty: you can submit only one HW late for 32 hours. Quizzes: (7+3)% x 3 = 30% and Midterm: (15+5)% = 20% Final Programming Project: 22% (project designed by me) Class Participation: 8% asking/answering questions in class and newsgroup catching/fixing bugs in slides/exams/hw & other suggestions 4

5 Academic Integrity an automatic F if you re caught on any of these: cheating during quizzes/exams catching cheating is easier than you thought! :-) copying another person s code for HW/Project copying code from online resources for HW/Project discussions with others for take-home quiz/exams any other cheating behavior defined by University I will report every single case to the University 5

6 Textbooks (for reference) but we will not follow any textbook. Textbooks How to Think Like a Computer Scientist: Learning Python by Allen B. Downey, Jeffrey Elkner and Chris Meyers strongly recommended! NLTK textbook by Steve Bird and Ed Loper (optional) Tutorials (Official) Python Tutorial by Guido van Rossum (inventor of Python) A Quick, Painless Tutorial on the Python Language by Norm Matloff 6

7 Course Outline 1. Python Basics Syntax, Control Flow -- quiz 1 Basic Data Structures (list, dict, tuple,...) -- hw 1 2. Object-Oriented and Functional Programming OOP (Objects, Inheritance,...) -- quiz 2 FP (map, filter, reduction, iters, lambdas) -- hw 2 3. Python for Algorithmic Problem Solving -- midterm 4. Combining Python and C/C++/Java -- hw3 5. Basic Text Processing using Python -- quiz 3 7

8 Why Python? Because it s easy and great fun! less than 10 years old, yet very popular now a wide-range of applications, esp. in AI and Web extremely easy to learn many schools have shifted their intro-courses to Python fast to write much shorter code compared to C, C++, and Java easy to read and maintain more English-like syntax and a smaller semantic-gap 8

9 On to Python...

10 C Java #include <stdio.h> Hello, World int main(int argc, char ** argv) {! printf( Hello, World!\n ); } public class Hello {! public static void main(string argv[])! {!! System.out.println( Hello, World! );! } } now in Python print Hello, World! 10

11 Printing an Array void print_array(char* a[], int len) {! int i; has to specify len, and only for one type (char*)! for (i = 0; i < len; i++)! {!! printf( %s\n, a[i]);! } } C for element in list:! print element only indentations no {... } blocks! or even simpler: print list for... in... :... no C-style for-loops! for (i = 0; i < 10; i++) Python 11

12 Reversing an Array static int[] reverse_array(int a[]) {! int [] temp = new int[ a.length ];! for (int i = 0; i < len; i++)! {!! temp [i] = a [a.length - i - 1];! }! return temp; } def rev(a): def...(...):! if a == []:!! return []...! else:!! return rev(a[1:]) + [a[0]] or even simpler: a.reverse() a without a[0] built-in list-processing function singleton list Java Python no need to specify argument and return types! python will figure it out. (dynamically typed) 12

13 Quick-sort public void sort(int low, int high) {! if (low >= high) return;! int p = partition(low, high);! sort(low, p);! sort(p + 1, high); } void swap(int i, int j) {!! int temp = a[i];! a[i] = a[j];! a[j] = temp; } int partition(int low, int high) {! int pivot = a[low];! int i = low - 1;! int j = high + 1;! while (i < j)! {!! i++; while (a[i] < pivot) i++;!! j--; while (a[j] > pivot) j--;!! if (i < j) swap(i, j);! }! return j; } def sort(a):! if a == []:!! return []! else:!! pivot = a[0]!!!! left = [x for x in a if x < pivot ]!! right = [x for x in a[1:] if x >= pivot]!! return sort(left) + [pivot] + sort(right) {x x a, x < pivot} how about return [sort(left)] + [pivot] + [sort(right)] Java Python smaller semantic-gap! got error?? 13

14 Python is... a scripting language (strong in text-processing) almost like pseudo-code! but also object-oriented (like C++ and Java) interpreted, like Perl, but much more elegant a very high-level language (closer to human semantics) procedural (like C, Pascal, Basic, and many more) and even functional! (like ML/OCaml, LISP/Scheme, Haskell, etc.) from today, you should use Python for everything not just for scripting, but for serious coding! 14

15 Let s take a closer look...

16 Python Interpreter Three ways to run a Python program 1. Interactive like DrJava >>> for i in range(5):... print i, (default) save to a file, say, foo.py in command-line: python foo.py 3. add a special line pointing to the default interpreter add #!/usr/bin/env python to the top of foo.py make foo.py executable (chmod +x foo.py) in the command-line:./foo.py 16

17 The right version of Python we will use the latest version 2.7 (e.g ) Python 3.x is a very different experimental branch... your default machine is cs12.cs.qc.cuny.edu, where your default python is already 2.7 or you can install 2.7 on your own mac/windows TA will help you with installations and versions bash-2.0$ python Python (#1, Jan , 18:59:00) [GCC (Apple Computer, Inc. build 1495)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> [<lhuang@mac OS X:~>] which python /Library/Frameworks/Python.framework/Versions/2.7/bin/python 17